回复：问个特别笨的问题， 620有几个有效数字？

Depends - see below. The key is to use scientific notation.

http://www.physics.uoguelph.ca/tutorials/sig_fig/SIG_dig.htm


Zeroes at the end of a number are significant only if they are behind a decimal point as in (c). Otherwise, it is impossible to tell if they are significant. For example, in the number 8200, it is not clear if the zeroes are significant or not. The number of significant digits in 8200 is at least two, but could be three or four. To avoid uncertainty, use scientific notation to place significant zeroes behind a decimal point:
8.200 ′ 103 has four significant digits
8.20 ′ 103 has three significant digits

8.2 ′ 103 has two significant digits